1. Field
This invention relates generally to networks used in automotive applications, and more particularly to power and control policies used in automotive data networks.
2. Related Art
Currently available power management and control policies used in automotive data networks are adapted from policies used in traditional data networks, such as enterprise systems, data centers, and access systems. Power management and control policies in both automotive communication networks and the traditional data networks focus on identifying the type of traffic (e.g. whether traffic is video or audio data) and on satisfying restraints imposed by applications running on networked devices (e.g. whether data to a mission critical application can be delayed). For example, current technology allows networked devices to be placed in a low power state when link utilization is low, i.e. there is little or no data traffic to or from the device. Likewise, when data traffic to or from a device has a low priority, the device can be placed in a low power state. If, however, link utilization is high, or the data traffic is high priority, the device is not placed in a low power state.
Various techniques are currently available for implementing low power states. For example, legacy Ethernet standards for interfaces of 100 Mbps generally incorporate an idle state that allows use of a low power state when link usage is low, but in practice only minimal power savings are achieved. Proposed IEEE 802.3az standard achieves power savings by sending only occasional transmission data bursts during a low power idle state. Proposed IEEE 802.3az standard also achieves power savings by powering down part of a network interface during the low power idle state. For higher speed Ethernet applications such as Gigabit Ethernet, some techniques achieve power savings by reducing the data transfer rate of one or more lanes of data, or by turning off some of the data lanes.
Regardless of the way in which a low power state is implemented, however, decisions about if and when to place a device in a low power state must still be made. This decision is complicated by the fact that a decision that incorrectly places a device in a low power state can cause unnecessarily long link startup and acquisition times. Similarly, a decision not to place a device into a low power state can result in unnecessarily high power usage. As previously mentioned, conventional power management and control policies focus on the amount of traffic being sent over a link, the type of traffic being sent over the link, or operating constraints imposed by applications running on networked devices. Use of these conventional network metrics may not result in optimum decision making in all situations. It is apparent, therefore, that currently available techniques for controlling the amount of power used by networked devices are less than perfect.